I was listening last night a string quartet rehearsal. The play was for the most part justifiably non-so-glorious and I was thinking about my little audio things. For sure our upper MF drivers nowhere near where they need to be. There is too much confusion out there as Jimmy Hendrix use to say. In my view the most limiting factor in audio to do more interesting MF are dynamic range and disorder of transients.

The 110dB that we achieve is a good dynamic range for a sustain tone but we need transients dynamic range that would have extra 6-12dB and we do not have it in audio. Any further increment of dynamic range comes with narrowing the radiation angle that very dramatically shrinks usable bandwidth. Than the upper octaves transients – they are the bitch as we have a lot of phase mess in the drivers, plus we have damping that eats transients like hell.

So, thinking more about it I come up with a notion of a new MF driver. It is a hypothetic driver, not something that you will run and buy off eBay. I post it as a concept, just to log my thoughts, if somebody has any further idea then be my guest.

So, pretend a vertical array of 5-6 narrow high-gain horn located on parabolic curve and strictly parallel. Why parabolic? Well, I shall not even mention time-alignment for this configuration – it goes without saying. The horns are very slow opening with the horns located on the peripheral of the array (in the position 1 and 6) have faster opening rate. Each horn run own very narrow bandwidth, let say ¾ of octave. Now is the key – the drivers are compression but do not use any damping. A few of you who have brain would read “no damping compression driver” and will ask if I am out of my mind. You will be right - “no damping compression driver” is a ridicules idea. A compression driver by nature is damped by mass of air in horn and by zillion of other factors. Still, I am taking about very new and very different concept. Let think about it.

They are MF horns, very small size, they care very little air in horn’s bell and have negligible throat reactance. If the driver has VERY strong magnet and VERY narrow bandwidth then it is possible do not damp it at all. So, I basic lay propose to custom made driver like a tuning fork (an acoustic resonator) or like a quartz oscillator – tuned for specific very specific octave. Now is the twist – the tuning of the driver have to follow the compression driver principle and it has to be tuned being loaded into the horn as the horn equalization need to be factored into the driver tuning.

So, we basically have 5-6 narrow miniature horns and 5-6 custom different size compression drivers with infinite back baffle and infinitely hard suspension. Sounds impossible, right? Well, how about to make those compression drivers to have infinitely loose suspension and to drive them with negative impedance? Then the driver will be damped in own operational bandwidth ONLY but the signal the drives it and will not be exposed to any suspension influence.

What I proposed will yield no damping will have around 118-119dB sensitivity and will yield max transient available by means of electro-mechanic. Probably MF plasma driver will be able to do more but one need another life to investigate all the options. Ironically what I propose is accomplishable and it would be VERY interesting to try it another day. My estimation is that to render the project like this for a person, including all listening test would take a year or two and probably another year or two to make this new MF array to work with the rest of playback. It might cost $30K-$50K expenses, plus a divorce and pay to psychologist (or most likely psychiatrist) to the rest of the life. Still, it is pretty conceptually is very interesting if not a project but at least idea.

I think the key is to develop some kind of prime, or some kind of algorithm according to which a bandwidth-tuned driver of n-octave might be made. Then, as a successful pattern was found the driver and horns of multiple sizes might be made. I am kind of too late in my life to undertake projects like this. I do feel sorry about it on another hand gratefully. Still, I love to think about it. Somebody out there has to push the envelope of possibilities and to keep the touch of advanced sound reproduction. I do not make claim that the array that propose will solve anything but unfortunately the only way to know it is to try. Yes, the high-end audio is the bitch…

Is this type of driver not similar to those used in headphone?. Very high efficiency, wide bandwidth, very low XMAX. The lightest and fastest are probably the orthodynamic type like FOSTEX RP, HiFiMAN or Audeze LCD2.

The AMT Heil driver had an interesting geometry that has much more surface area due to the accordian principle. At the time this technology was new, they had much extended output and bandwidth due to the higher acceleration possible with this unique geometry. They claimed 5 times higher transient response. I believe that Linn also had a pair of woofers in a cabinet facing each other for the same reason. It seems to me that this could be a possible solution, either with multiple drivers or a new driver geometry that allows for better transient response.

I do not like the AMT Heil drivers at all. I have no idea what 5 times higher transient response they claimed but to my ears all AMT drivers I heard sounded like their upper notes are covered with 2 inch deep saliva. The Heil drivers are in my view the ultimate “girls with banjo” type of drivers and surprise that 99% audio people love AMT as they do not accustom to listening anything more sophisticated than “girls with banjo”. Heils convert any note higher than the double high C into some kind of generic Vaseline-covered HF note. They do sound “impressive” with American Steel Guitars but actually if the demands to sound are higher than average Saturday white-trash listening under beer then there is absolutely no help from Heils.

Take any chromatically-complex music and Heils will make all upper notes to sound identical. Who need that type of performance from audio?

I have not heard the Heils with all possible amps, but to my ears they are equally unequivocal with Tone and Dynamics, once their (rather low) "threshold" is reached. At least with respect to dynamics, this seems like the opposite of what one would aim for with compression drivers (re: the header). Sure, a bad or "un-tuned" (ie, typical) compression driver will choke up, but at least the topology is dynamically proven. If there are specific Heils (or, of this ilk) that serve a Higher Calling, I hope someone will call attention to them.

Too many drivers that start out with "fast" transients quickly fade into oblivion. Other topological examples of this behavior are ribbons and 'stats. Most drivers, including compression drivers, are "non-linear", in the sense that their performance typically varies according to the demands of the Music; but some drivers pretty much never get off the ground.

I have heard some nice speakers in Germany using the Mundorf Air Motion Transformers. No saliva, ample "substance" in their tone and a very nice integration.http://www.mundorf.com/AMTnews/MUNDORF_PRO_AMT_FLYER_2012.pdfhttp://www.enjoythemusic.com/superioraudio/equipment/0212/jaton_real_a3.htmI am not defending the principle, it just seems like a compression chamber could be fed by opposed drivers with an exit 90° to the driver direction IF the distance between the driving surface is considerably less than the wavelength of the highest frequency required.

Robin, of course I meant to say above that the Heils are equivocal when pressed, and no reason for me to think a compression chamber mosh with another driver would improve this quality; but I am just guessing. It would certainly be interesting if you were to put your idea to the test. Would you opt to feed two motors into a single radiator, or...?

What did you like about the Mundorfs that you "hear" bettered by combining them as you suggest?

What sort of music did you hear them render, and what sort of amps did/do they require?

I have heard some nice speakers in Germany using the Mundorf Air Motion Transformers. No saliva, ample "substance" in their tone and a very nice integration.http://www.mundorf.com/AMTnews/MUNDORF_PRO_AMT_FLYER_2012.pdfhttp://www.enjoythemusic.com/superioraudio/equipment/0212/jaton_real_a3.htmI am not defending the principle, it just seems like a compression chamber could be fed by opposed drivers with an exit 90° to the driver direction IF the distance between the driving surface is considerably less than the wavelength of the highest frequency required.

That 10-12 inch tall driver is an interesting beast. I never heard the Mundorf’s drivers, never even heard about them. It is possible that they use new and much thinner film that made Mundorf to sound differently then rest AMT. Still, I do not think that topologically any AMT or planar might beat the freedom of naked ribbons. I do appreciate your feedback, Robin, but I still do have my reservations based upon my former experience with AMT.

Saying that, I still do feel that this tallest Mundorf is interesting for the guys like me. If you are in Macondo configuration then this type of driver is a very interesting solution. The 105dB sensitively (if it is true) made it to match classic 109-110dB sensitive MF channels and that is very good.

Sure I would be more open if Mundorf do not shot for absurd for me 2.5kHz crossover point and for 1000W power handling, not to mention the forced air cooling. But it is what it is and I think that the largest Mundorf might be added to the list of Macondo configuration computable candidates. I still think that a long exposure to Mundorf’s AMT will reveal the deep intrinsic AMT illnesses but as I get neither of us are not familiar with big Mundorf well.